Birds are warm-blooded vertebrates that have feathers to insulate and protect their bodies. In most species of birds, feathers are also important adaptations for flying. As a general rule, birds devote a lot of time and energy to keeping their feathers waterproof in a process called preening. During preening, birds rub their feet, feathers, and beaks with oil produced by the preen gland near their tail.
The strong, lightweight bones of birds are especially adapted for flying. Many of the bones are fused, resulting in the rigid type of skeleton needed for flight. Although birds are not very good at tasting or smelling, their senses of hearing and sight are exceptional. They maintain a constant, relatively high body temperature and a rapid rate of metabolism. To efficiently pump blood around their bodies, they have a four-chambered heart.
Like marine reptiles, marine birds have glands that remove excess salt from their bodies. Although the structure and purpose of the salt gland is the same in all marine birds, its location varies by species. In most marine birds, salt accumulates in a gland near the nostrils and then oozes out of the bird’s body through the nasal openings.
The term seabird is not scientific but is used to describe a wide range of birds whose lifestyles are associated with the ocean. Some seabirds never get further out into the ocean than the surf water. Many seabirds are equipped with adaptations of their bills, legs, and feet. Short, tweezerlike bills can probe for animals that are near the surface of the sand or mud, while long, slender bills reach animals that burrow deeply. For wading on wet soil, many seabirds have lobed feet, while those who walk through mud or shallow water have long legs and feet with wide toes.
Other marine birds are proficient swimmers and divers who have special adaptations for spending time in water. These include wide bodies that have good underwater stability, thick layers of body fat for buoyancy, and dense plumage for warmth. In swimmers, the legs are usually located near the posterior end of the body to allow for easy maneuvers, and the feet have webs or lobes between the toes.
All marine birds must come to the shore to breed and lay their eggs. Breeding grounds vary from rocky ledges to sandy beaches. More than 90 percent of marine birds are colonial and require the social stimulation of other birds to complete the breeding process. Incubation of the eggs varies from one species to the next, but as a general rule the length of incubation correlates to the size of the egg: Large eggs take longer to hatch than small ones do.